Aqueous bleaching agent suspensions containing peroxycarboxylic acids are known from British Pat. No. 1,535,804, corresponding to U.S. Pat. No. 3,996,152 and U.S. Pat. No. 4,017,412. Such bleaching agent compounds can be added with advantage to alkaline washing mixtures in washing machines or be used as bleaching agents.
The use of bleaching agent suspensions, in comparison to solid, generally particulate bleaching agent compounds, has the advantage of being able to eliminate expensive and, in the case of peroxycarboxylic acids, drying and granulating steps which may not be reliable. However, in addition to being effective in use, bleaching agent suspensions must satisfy certain essential conditions which are needed for smooth and reliable handling in commercial and domestic areas. These conditions include good chemical stability and especially physical stability as regards a solid liquid phase separation and handling safety even in the case of leakage or spaying of the suspensions from barrels.
The aqueous bleaching agent compounds according to British Pat. No. 1,535,804 contain essentially water-insoluble peroxycarboxylic acids which are suspended in an aqueous carrier liquid containing a thickening agent. These compounds are thickened until gelled and their viscosity is 200 to 100,000 centipoises. Starches, cellulose derivatives, natural rubbers, synthetic organic polymers as well as inorganic thickening agents of the group of colloidal silicic acids and hydrophilic clays are claimed as thickening agents.
A major disadvantage of the known bleaching agent compounds of British Pat. No. 1,535,804 is their usually completely insufficient storage resistance, as least to the extent that they are not gelled systems. The suspensions are physically unstable since the solid phase separates from the liquid phase. This instability usually becomes noticeable directly after preparation of the suspension, frequently within one day or even hours. On the other hand, experts in this field call for a greater storage resistance, preferably one of several weeks.
Another disadvantage caused by the physical instability concerns the redispersibility of the thickened phase containing the peroxycarboxylic acid, which is unacceptably difficult. Finally, bleaching agent suspensions prepared with a low concentration of a thickening agent present an increased potential for danger because, after a suspension has been spilled, and especially after the spilled material has dried substantially non-desensitized peroxycarboxylic acid remains.
There has been no lack of attempts to create bleaching agent suspensions with improved storage resistance and a lesser potential for danger. Thus, published European patent application EP-A No. 0,160,342 teaches aqueous bleaching agent suspensions in which water-insoluble peroxy acids are suspended in an aqueous liquid containing a surfactant and an electrolyte. The limited chemical stability of these surfactant-structured suspensions was able to be improved according to the teaching of published European patent applications EP-A No. 0,176,124 and EP-A No. 0,201,958; nevertheless, they do not satisfy the requirements of physical stability placed on them.
British Pat. No. 1,535,804 disclosed the use of colloidal silicic acids, especially pyrogenic silicic acids. In order to obtain the desired thickening, however, a supplemental amount of 10 to 50% by weight, in relation to the suspension, is required. However, such a high added amount of high-grade, generally very expensive pyrogenic silicic acids is extremely uneconomical, so that there is still a need for improved bleaching agnet suspensions.